Aging is accompanied by a decrease in aminergic function and a decrease in the speed of information processing. Stimulant drugs speed performance on a wide variety of cognitive tasks in young subjects. In older subjects they speed performance only on certain tasks. This suggests that in old subjects some cognitive processes are slowed, some processes are speeded by stimulants and these stimulant sensitive stages may or may not be the same as those that decline with age. Changes in aminergic function and speed of information processing are also observed in the dementias. An understanding of the mechanisms which underlie stimulant effects in the elderly may be important in understanding cognitive declines with normal aging and dementia. The purpose of this proposal is to determine the interrelationship between aminergic neurotransmitter function, human information processing (HIP) and normal as well as pathological aging. The goals are 1) to specify the nature and extent of aminergic effects on HIP in elderly subjects, 2) to determine how stimulant drugs affect HIP in Alzheimer and other dementias, 3) to determine the relative contributions of the norepinephrine (NE) and dopamine (DA) systems to HIP and 4) to refine our present work on the role of the NE and DA systems in mediating stimulant drug actions. These goals will be pursued by examining the effects of aminergic agonists and antagonists in several ways. First, we will isolate the task, drug, dose and time of testing variables which are important in obtaining stimulant effects in normal elderly. The results of this study then will be used to design experiments to investigate the effects of stimulant probes in individuals with Alzheimer's Disease (SDAT) and vascular dementias (SDCV). Finally a series of NE and DA probe experiments will be conducted using normal young adults. These studies will examine the effects of various agonists and antagonists alone and in combination with stimulants to determine whether the improvement in HIP with stimulants can be attributed to one or the other of these neurochemical systems. All studies use tasks with well defined sequential information processing stages. The additive factors method (AFM) is used to localize the effects of age and drug on specific stages. Dependent variable include reaction time and the latency of P300 component of the event related potential (ERP). The latter measure provides a converging measure of HIP that is sensitive to stimulus evaluation processes. The effects of drugs and of aging on the information processing sequence are inferred from the interactions between experimental variables on RT and P3.